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RAPTOR Frequently Asked Questions
What is the RAPTOR's ability to detect non-viable virus or inactivated toxins?
The short answer to your question is, 'it depends.' Our baseline methods use sandwich immunoassays. If the inactivation process does not destroy the surface structures that the antibody specifically binds to, then non-viable and inactivated materials would test the same as viable or active materials. If the surface is severely distorted or denatured, then sensitivity would be reduced. As real-life examples;
- Heat-killed (boiled) and live E Coli O157-H7 produce almost identical responses, but-
- Ricin toxoid, which is ricin with the toxic portion of the molecule cleaved off, produces only about 1/100 the signal of natural ricin. Viral coats are reasonably stable, so our guess would be that most viruses would mimic the E Coli experience, but that the response of an inactivated toxin would need to be empirically determined.
Is it possible to quantify the RAPTOR assay analysis?
Yes. What you do is challenge the coupon with a range of concentrations of the target analyte, and in that way obtain a response curve. While the unit will not compute concentrations directly, the data can be downloaded and the data compared with the response curve. If you had a customer that was going to buy a large number of units, we could provide custom software (hopefully, paid for by the user) that allowed you to load a response curve into the BioHawk (or RAPTOR) and which would provide a numeric output. Users generally prefer to stay away from numeric outputs, as field operators usually are more interested in and capable of understanding presence/absence, rather than actual concentration.
Has the U.S. Department of Homeland Security Safety Act Certified any portable biological detectors other than the RAPTOR?
There is only one – the Razor, a real-time PCR system from Idaho Technology, Inc. At present it is a manually operated system and cannot be set up for unattended site monitoring. It is a bit more sensitive for viruses and bacteria, but is totally blind to toxins since it requires that nucleic acids be present. That is the real Achilles heel of the nucleic acid systems – they cannot directly detect targets like ricin.
Please explain in detail why the disposable waveguide probes can be re-used up to 20 times? Once a virus is detected does the waveguide probe need to be thrown away?
The waveguides are coated with a target-specific antibody. If the target is not present in a sample, the coating is still good, and is available for further sample challenges. The coating is stable for maybe 24-48 hours, depending on temperature, the presence of chemicals that might cause the antibodies to become damaged, or bacteria that might like to eat the antibody coating. The secondary fluorescent reagent is stored and reused, so its life is long as well. It does not attach to the waveguide unless the target substance is present in the sample, so it is not depleted except through dilution.
Once one of the waveguides has captured some of its targeted substance, that particular waveguide is compromised, but the other waveguides (assuming they target something else) would still be unaffected. Subsequent assays may show a small positive response on that channel, even if there is no targeted substance present in later samples, due to the fact that the secondary antibody reaction is not 100% effective at labeling each captured target on the first use. This is a conscious choice on our part. By not going to equilibrium on the step where the waveguide is soaked in the secondary antibody, the assay time is significantly shortened.
We use sandwich assays to detect viruses, do we use the same principle to detect chemicals like Sarin?
Sarin is too small a molecule to be detected. Usually, a molecule has to have a molecular weight of over 500 to have enough surface structure to be recognized by an antibody. Sarin only has a molecular weight of 140. It might be possible to engineer non-antibody based assay reactions for analytes such as Sarin, but such an option is not currently offered.
Please explain the difference between array, coupon and recipe.
An "array" is usually a grouping of discrete chemical reaction sites. A "coupon" is a disposable credit card-sized assay module that has fluidics and chemistry integrated together. It would have an array of capture antibody sites and fluidic channels connecting the sites to the instrument. In the BioHawk coupon, it additionally stores the secondary antibody reagent as well in small onboard reservoirs.
A "recipe" is a series of instrument operations that together, allow a user to perform an assay under total computer control. In general, these operations include turning pumps and valves on and off for programmed times, turning interrogating lasers on and off for programmed times, storing samples for confirmatory analysis, and performing aerosol sample collection for a programmed time.
